Biography
鬼 (Oni) are brutish mountain Youkai superficially similar to Trolls and Ogres, with either one or two horns (which in some depictions are the source of their power). The word is almost always translated into English as "demon" or (especially in older translations) "ogre". However, while large, strong, and often brutish, Oni can also wield powerful magic and are usually depicted as more intelligent than Western ogres. Further, certain types are very calm and introspective, and female oni, being very beautiful, can get along well with (and sometimes marry) humans. While oni as a title has connotations similar to "demon" or "maniac", works depicting literal oni may show them as either good or bad, often being morally neutral and interested in their own affairs. They prefer huge bludgeoning weapons (iron clubs called kanabō being the most common) and hide loincloths (usually tiger-striped). They are also shown to really love their alcohol, which can make them even more rowdy. Sometimes blamed for streaks of misfortune or violent weather. Others work jobs in Fire and Brimstone Hell as big red devils.
If Oni come in pairs, there's a good chance one will be red and the other blue. However, they won't always match the Red Oni, Blue Oni dynamics. If some Oni are explicitly female, Bizarre Sexual Dimorphism may occur with males looking Gonky and the females looking more conventionally attractive. Which is consistent with their mythological descriptions.
"Oni" originally referred to misfortune, bad vibes and evil spirits, which were traditionally said to come from the northeast. Under the Eastern Zodiac this is known as the "ox-tiger" direction, so these forces came to be anthropomorphised as beings with features of oxen and tigers note . Figures clad in tiger pelts are also associated with Super Strength across Asia, where tigers are the traditional equivalent of the King of Beasts.note Because they're Made of Evil (or at least Made of Chaos), even non-dangerous supernatural powers used by oni tend to automatically qualify as Black Magic or Curses.
Sometimes particularly wild and brutish humans are depicted as transforming into oni as they are warped by the foul energies surrounding them. At some points in Japanese history the word "oni" became practically synonymous with "barbarian", and conquering or pacifying territories was described as "ridding lands of oni".
Particularly powerful oni may be described as 鬼神 (kishin, literally "oni god"), a term used in Japanese Buddhism to refer to Wrathful Deities, while in some instances the term 悪鬼 (akki, literally "evil oni") specifically design evil-minded, man-eating oni. Incidentally, the Japanese word for vampire (吸血鬼 kyuuketsuki) can be translated as "blood-sucking oni"; see here for details.
Hyakki Yakou, the Japanese equivalent of The Wild Hunt, literally translates as "Night Parade of 100 Oni", though this usage is metaphorical (most depictions of the Parade include a wide variety of Youkai) and is usually glossed as "demons" even when oni is otherwise left untranslated. That said, it has lead to a number of works that use some variant of "Hyakki" (or worse, "Senki"note ) as a name or title for a particularly powerful oni; in more literal cases they may even be 100 demons fused together into an Eldritch Abomination.
Compare Horned Humanoid and Wild Man. For the Oni's Western counterparts, see Our Ogres Are Hungrier and All Trolls Are Different (and occasionally Our Demons Are Different). See also Monster Lord for when oni are treated as an "evolved" form of ogres.
See also Smash Mook (a common archetype for oni in video games).
